1. Field of the Invention
One embodiment of the invention disclosed herein relates to a power receiving device and a power feeding system.
2. Description of the Related Art
Various electronic appliances have spread, and a variety of products are shipped to the market. In recent years, portable electronic devices such as mobile phones and digital video cameras have widely spread. Further, electric propulsion moving vehicles that are powered by electric power, such as electric cars, appear on the market as products.
In such mobile phones, digital video cameras or electric propulsion vehicles, power storage devices serving as power storage means (referred to as batteries and storage batteries) are incorporated. Currently, power feeding to such a power storage device is performed in most cases by direct connection to a household AC power source which is a power feeding means. In addition, a structure without a power storage device or a structure which does not use electric power fed to a power storage device is directly fed with power from a household AC power source through a wiring or the like so that a unit operates.
On the other hand, methods by which electric power is fed to power storage devices without making contact or electric power is fed to loads without making contact have been researched and developed. Typical methods are an electromagnetic coupling method (also referred to as electromagnetic induction method, see Reference 1), a radio wave method (also referred to as microwave method), and a magnetic resonant method (also referred to as resonant method, see References 2 to 3).
As described in References 2 to 4, in a contactless power feeding technique using a magnetic resonant method, a device that receives electric power (hereinafter, referred to as power receiving device) and a device that supplies power (hereinafter, referred to as power transmitting device) each have a resonant coil. Further, in each of the power receiving device and the power transmitting device, an electromagnetic induction coil is provided. Power feeding from a power source to the resonant coil of the power transmitting device and power feeding from the resonant coil to a load of the power receiving device are conducted through the electromagnetic induction coils.
The resonant frequencies (LC resonance) of the resonant coils of the power transmitting device and the power receiving device are set to be the same so that a magnetic resonance phenomenon is produced at a specific frequency.
When the resonant coils of the power transmitting device and the power receiving device face each other, they make a magnetic resonance phenomenon, and thereby efficient power transmission is achieved even when the distance between the resonant coils is large (see non-patent document 1).